1. Field of the Invention
The present invention relates to a radio apparatus and, specifically, to a radio apparatus as one of a plurality of radio apparatuses constructing an ad-hoc network in an autonomous and instantaneous manner.
2. Description of the Related Art
An ad-hoc network is a network constructed in an autonomous and instantaneous manner by a plurality of radio apparatuses communicating with each other. In the ad-hoc network, when two radio apparatuses to communicate with each other do not exist in a mutual communication area, a radio apparatus located at an intermediate position between the two radio apparatuses functions as a router and relays a data packet, whereby a wide area multi-hop network can be formed.
Applications of the ad-hoc network as such are expected in various fields, including wireless communication network at a disaster site and streaming in vehicle-to-vehicle communication in ITS (Intelligent Transport Systems) (Shozo Komaki (Ed.), “Wireless LAN and Ubiquitous Network”, Maruzen Kabushiki Kaisha, 2004).
Dynamic routing protocols supporting multi-hop communication include table-driven type protocols and on-demand type protocols. According to the table-driven type protocol, control information related to routes is exchanged on a regular basis, and a route table is formed in advance. FSR (Fish-eye State Routing), OLSR (Optimized Link State Routing) and TBRPF (Topology dissemination Based on Reverse-Path Forwarding) are known examples.
According to the on-demand type protocol, a path to an address is formed for the first time when a data transmission request is generated. DSR (Dynamic Source Routing) and AODV (Ad Hoc On-Demand Distance Vector Routing) are known examples.
In the conventional ad-hoc network, for a data communication from a source to a destination, a communication path is determined such that the hop number from the source to the destination is made as small as possible (Shozo Komaki (Ed.), Wireless LAN and Ubiquitous Network, Maruzen Kabushiki Kaisha, 2004).
The current ad-hoc network, however, does not allow simultaneous transmission/reception of packets using the same frequency channel. Further, it is not possible, either, to set up a network across different frequency channels.
As a result, while a radio apparatus in an ad-hoc network is receiving packets, the radio apparatus and neighboring radio apparatuses cannot transmit packets at the same time.
Therefore, when there are a plurality of data flows in multi-hop transmission, it follows that transfer delay derived from waiting accumulates at every relay, eventually resulting in a considerably large delay, and the delay of the ad-hoc network undesirably increases.
Further, in the current ad-hoc network, it is not expected that the route is always maintained in a stable manner, and therefore, a route search is performed on a regular basis or on-demand, to update a route selection table. Accordingly, the routing process is accomplished as a software process by Layer 3, which tends to cause process delay.
Further, when we consider flooding in which packets are transmitted to an unspecified number of radio apparatuses in the ad-hoc network, an identifying process is necessary to avoid duplicate packet transmission, and such identifying process also causes process delay.